Non-invasive detection of the concentration of a certain component within a substance especially human tissue represents great importance in clinical medicine, and in particular, non-invasive detection of the concentration of blood glucose within human body plays a key role in diabetic diagnosis. Till now some related non-invasive detection instruments have been successfully developed by some research institutions in Japan, USA and Western Germany, etc. For most of these non-invasive detection instruments, NIR spectroscopy is applied, wherein because different components within a substance especially human tissue possess different light absorption coefficients in NIR range, the concentration of one or several target components can be detected through analyzing the measured absorption spectra. U.S. Pat. No. 5,348,003 is an example introducing a method and instrument using continuous spectra for non-invasive detection of the concentration of multiple components in a substance; in U.S. Pat. No. 5,028,787, a method and instrument for non-invasively detecting blood glucose concentration through analyzing continuous spectra is presented; in Japanese Registered Utility Model Applications NO. 2588468, an LED with its wavelength ranging from 1.4 to 1.7 μm is used as a light source for non-invasive detection; in Japan Patent Publication No. 8-27235, a setup for chemical analysis is presented using single-wavelength laser. In all these non-invasive detection methods or instruments, a continuous light source or discrete light source is used to create NIR spectra, whereas none of those instruments produce NIR spectra via a composite light source combining continuous light source with discrete light source.
Because generally the absorption wavelength ranges of different components within a substance especially human body overlap, when detection is conducted using a discrete light source that emits single-wavelength light, only overlapped biological information at certain wavelength can be obtained, while information at other wavelengths is very difficult to get. This means, to make a stable and quantitatively non-invasive detecting system, it is a must to achieve high sensitivity, high precision and good accuracy in a considerably broad spectral range, and thus measurement can not take place at a discrete spectrum of a single wavelength or a specific frequency. Firstly, spectra under multiple wavelengths should be obtained. Then by stoichiometric modeling method, the concentration of components of interest can be calculated. In this multiple wavelength spectral measurement, a continuous light source comprises of, for example, a halogen lamp and a light-splitting system, or wavelength tunable laser, or several discrete wavelength LDs, or an interference filter. However, there are not so many LDs, and therefore corresponding products do not exit at each wavelength. Furthermore, each filter has a fixed wavelength. To satisfy the requirement for each wavelength, a considerable number of filters should be used, making the cost of the whole system very high. This is why the method using continuous light source is often appreciated. Consider that the wavelength range is still limited even after the continuous light source passing a light-splitting system and that, because multiple target components within the substance demonstrates strong absorption toward the spectra, e.g., in blood glucose concentration detection, water has great absorption toward NIR spectra, or because the energy of the spectra of the continuous light source is relatively low, the energy of NIR spectra is not enough for the measurement, and in particular, the spectra of the continuous light source may lack some certain NIR spectra that are sensitive to the target components. All these factors obviously make useful information of target components (e.g., blood glucose) that the absorption spectra carry become weaker and directly influence the accuracy, stability and SNR of the detecting system, and thus, it is necessary to introduce one or several discrete light sources plus the continuous light source to form a composite light source, and by the combination of spectra measured by different light sources, composite spectra with high accuracy can be achieved to realize non-invasive detection.
The accuracy of current non-invasive detectors can not meet clinical application requirement, mainly because it is difficult to simultaneously achieve high energy at both multiple wavelengths and at each wavelength in the detecting system. However, through utilizing composite spectra achieved by a composite light source both multiple wavelengths and high energy can be obtained, so that the SNR of the quantitatively non-invasive detecting system can be enhanced, and non-invasive detection of the concentration can be realized.